svn commit: r357570 - head/sys/kern

[Leandro Lupori]

Author: luporl
Date: Wed Feb  5 11:34:10 2020
New Revision: 357570
URL: https://svnweb.freebsd.org/changeset/base/357570

Log:
  Add SYSCTL to get KERNBASE and relocated KERNBASE
  
  This change adds 2 new SYSCTLs, to retrieve the original and relocated KERNBASE
  values. This provides an easy, architecture independent way to calculate the
  running kernel displacement (current/load address minus original base address).
  
  The initial goal for this change is to add a new libkvm function that returns
  the kernel displacement, both for live kernels and crashdumps. This would in
  turn be used by kgdb to find out how to relocate kernel symbols (if needed).
  
  Reviewed by:	jhb
  Differential Revision:	https://reviews.freebsd.org/D23284

Modified:
  head/sys/kern/link_elf.c

Modified: head/sys/kern/link_elf.c
==============================================================================
--- head/sys/kern/link_elf.c	Wed Feb  5 11:02:00 2020	(r357569)
+++ head/sys/kern/link_elf.c	Wed Feb  5 11:34:10 2020	(r357570)
@@ -51,6 +51,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/fcntl.h>
 #include <sys/vnode.h>
 #include <sys/linker.h>
+#include <sys/sysctl.h>
 
 #include <machine/elf.h>
 
@@ -389,6 +390,13 @@ link_elf_link_common_finish(linker_file_t lf)
 
 extern vm_offset_t __startkernel, __endkernel;
 
+static unsigned long kern_relbase = KERNBASE;
+
+SYSCTL_ULONG(_kern, OID_AUTO, base_address, CTLFLAG_RD,
+	SYSCTL_NULL_ULONG_PTR, KERNBASE, "Kernel base address");
+SYSCTL_ULONG(_kern, OID_AUTO, relbase_address, CTLFLAG_RD,
+	&kern_relbase, 0, "Kernel relocated base address");
+
 static void
 link_elf_init(void* arg)
 {
@@ -431,6 +439,7 @@ link_elf_init(void* arg)
 #ifdef __powerpc__
 	linker_kernel_file->address = (caddr_t)__startkernel;
 	linker_kernel_file->size = (intptr_t)(__endkernel - __startkernel);
+	kern_relbase = (unsigned long)__startkernel;
 #else
 	linker_kernel_file->address += KERNBASE;
 	linker_kernel_file->size = -(intptr_t)linker_kernel_file->address;